text: To make lengths of HDPE pipe, polyethylene raw material is dried, heated to ~, and extruded through a die. 
  Polyethylene pipe is usually black due to the addition of 3-5% of carbon black to the clear polyethylene material, which adds UV light resistance to the finished pipe. To create striped HDPE pipe a different die is used, containing small channels that the colored material runs through just before it is pushed through the die. Co-extruded, or co-ex HDPE pipe has an extra skin of color around the black HDPE pipe, allowing the pipe to be colored on the outside for the identification of thermal cooling requirements.
  After coming through the die the pipe is cooled by submerging in or spraying with water. The rate of cooling is carefully controlled to avoid deformation of the extruded pipe. Once cooled, a laser or powder printer prints the size, type, date, and manufacturer's name on the side of the pipe. It is then cut by a saw cutter or coiled into longer lengths on a coiler.